Spheres of Power is good for making all sorts of interesting magic systems. You could do this pretty easily with that system that's how I would actually do it.
Alternatively you could do something like at will abilities but require metal, maximum number of charges that you can store equal to twice your con modifier or something:
Allomancy
Allomancers store metal in there bodies to gain special powers, one bead of metal holds 1 charge an allomancer can hold their constitution modifier in charges in their stomach. If they have more they become sickened, eating a new bead is a move action and the charge cannot be used in the round immediately after being swallowed.
Coin-shot (steel)
As a swift action you may burn 1 bead of steal to gain the ability to push on metals for a number of minutes equal to your con modifier. With this ability you can perform the following actions.
1. As a standard action make a ranged attack with a coin as if it was a shuriken with a range increment of 60 ft, you can fire up to three at a time apply your constitution modifier to the damage from each coin.
2. As a standard action make a bullrush attempt vs a foe wearing metal within 60 ft using your Constitution modifier instead of your strength modifier
3. As a move action you can ready yourself to deflect metal projectiles until the start of your next turn you can deflect all metal projectiles aimed at you for one round.
4. As a standard action push against something metal and larger than you like a building or a metal statue to launch yourself through the air up to 60ft in a straight line away from your anchor. This does not grant flight and landing is up to you (acrobatics check).
Lurcher (iron)
As a swift action you may burn 1 bead of steal to gain the ability to pull on metals for a number of minutes equal to your con modifier. With this ability you can perform the following actions.
2. As a standard action make a bullrush attempt vs a foe wearing metal within 60 ft using your Constitution modifier instead of your strength modifier this effect pulls the target towards you.
3. As a move action you can ready yourself to pull all metal projectiles that pass within 30 ft of you towards yourself for one round, if you are using a shield you can pull them all into your shield and take no damage.
4. As a standard action pull something metal and larger than you like a building or a metal statue to launch yourself through the air up to 60ft in a straight line towards your anchor. This does not grant flight and landing is up to you (acrobatics check).
Thug (Pewter)
As a swift action you may burn 1 bead of pewter to gain enhanced physical prowess. With this ability you can perform the following actions.
1. As a swift action burn one bead to gain +2 to str dex and con for 1 min per constitution modifier.
2. As a swift action burn one bead to gain +4 to str dex and con for 1 round per constitution modifier.
Tineye (Tin)
As a swift action you may burn 1 bead of pewter to gain enhanced physical senses. With this ability you can perform the following action.
1. As a swift action burn a bead of Tin to gain low-light vision, and gain +10 to all perception checks for 1 hour per constitution modifier.
Rioter/Soother (Zinc/Brass)
As a swift action you may burn one bead to influence people for 1 min per constitution modifier.
1. When affecting a crowd you may grant a +/-5 bonus to any attempt to influence the crowd made by you or someone else (bluff, diplomacy, intimidate, etc.)
2. When affecting an individual you may grant a +/-10 bonus to any attempt to influence the individual made by you or someone else (bluff, diplomacy, intimidate, etc.)
Seeker (Bronze)
As a swift action you may burn a bead of bronze to automatically detect all allomancy not within a copper cloud within 60ft for 1 min per constitution modifier.
Smoker (Copper)
As a swift action you may burn a bead of copper to hide all allomancy within 60ft from a seeker for 1 hour per constitution modifier.
Throw in some feats to expand and refine abilities and your almost there!
Some good thoughts there, though I think that the number of charges might be on the low side (for example, a mistborn couldn't even hold a standard mix without being superhuman).
Yah it would need refinement. Maybe twice constitution modifier in charges and mistborn get twice con score instead. Really mistborn are so powerful you would need a whole class for it to be anywhere near balanced with a mistling.
It also doesn't account for some abilities having an apparently different use cost, such as a Lurcher burning iron at a low rate to see sources of iron in the area.
I accounted for different "burn" rates by adjusting the duration of abilities that you get from one charge. Would need to add a detect metal thing for lurchers and coinshots probably 1 charge for con modifier hours or something.
Using your ideas, you'd want the person to use a feat in order to use things like the reflexive dodging we see Coinpushes and Lurchers do on a regular basis?
I would have feats for finer uses of power like add scent or tremorsense to tineye and always blocking/deflecting projectiles without readying an action for lurchers/coinshots.
There are a few considerations here, the primary concern being that unless metal in your setting is a heavily-regulated commodity with a strict government, metal will be very plentiful.
Another consideration is whether allomancy is very prevalent. If it is, then your answer to the previous question should be influenced by this. The more prevalent allomancy is, the more work will be done to keep metal supply regulated.
I had another one but I forgot.
As for implementation, I would make an Allomancy (steel) skill for "pushing," Allomancy (iron) for "pulling," and so on... This can allow for a range of target DCs for slow burning or "flaring." Any DCs I would provide would be arbitrary, but if you want to use skills as a stand in, I would recommend working them out for how you want them used. (Obviously, easier DCs will make for more frequent usage.)
Using metals as what will basically amount to spell components, refilling them on a regular basis might be a solution? This really depends on the setting.
Hope that my thinking was of some use to you! Good luck and happy gaming!